Crystal structure of tris{N,N-diethyl-N′-[(4-nitrophenyl)(oxo)methyl]carbamimidothioato}cobalt(III)

The synthesis, crystal structure and a Hirshfeld surface analysis of tris{N,N-diethyl-N′-[(4-nitrophenyl)(oxo)methyl]carbamimidothioato}cobalt(III) are described.


Chemical context
Thiourea derivatives and their metal complexes have been of interest for the past two decades.Recent reviews have highlighted current trends in their chemistry (Zahra et al., 2022;Saeed et al., 2014) including medical and chemosensing applications (Khan et al., 2021).One older study evaluated the potential of N-benzoyl-N 0 -dialkyl derivatives and their Co III complexes as antifungal agents (Wiequn et al., 2003(Wiequn et al., , 2005)).The synthesis of these later complexes are straightforward: mixing three equivalents of the ligand with CoCl 2 •6H 2 O in water and stirring for an hour results in deposition of the neutral, dark-green Co III complexes.Making the analogous tris-coordinated complexes was not our original intention.In the course of preparing Co III complexes coordinated by a single � 2À S,O ligand, the neutral tris product was invariably formed as a side product when reacting the labile Co III starting material [(en) 2 Co(OSO 2 CF 3 )]CF 3 SO 3 (Dixon et al., 1981) with one equivalent of ligand.This paper presents the synthesis and crystal structure of tris{N,N-diethyl-N 0 -[(4-nitrophenyl)(oxo)methyl]carbamimidothioato}cobalt(III), I.

Structural commentary
The molecule of I consists of three N,N-diethyl-N 0 -[(4-nitrobenzene)(oxo)methyl]carbamimidothioato ligands, each bound to a single Co III centre by their sulfur and carbonyl oxygen atoms.The complex has crystallographic threefold symmetry, with the Co III atom (Fig. 1

Supramolecular features
There are no conventional hydrogen bonds in the in the crystal structure of I.There are, however, three weak hydrogen-bondtype interactions with C-H donors and S or O acceptors (Table 2).Of these, only the C9-H9B� � �O3 iv [d D� � �A = 3.213 (2) A ˚] and C7-H7A� � �S1 iii [d D� � �A = 3.8362 ( 19) A ˚] (symmetry codes as per Table 2) contacts are intermolecular.The former (and their 3-symmetric equivalents) link groups of six molecules into puckered ring assemblies about the c-axis, which create and confine the solvent-accessible channels that extend along [001] (Fig. 2).Attempts to create an unambiguous model for the solvent within these channels were unsatisfactory (see section 6, below).Individual molecules loosely stack into columns that propagate parallel to [001] via the C7-H7A� � �S1 iii (and their symmetry equivalent) interactions (Fig. 3).Adjacent columns are antiparallel (i.e., along An ellipsoid plot (30% probability) of I. Unlabelled atoms correspond to symmetry codes: (i) À y + 1, x À y + 1, z; (ii) À x + y, À x + 1, z, as indicated by the superscripts on the O and S atoms of the symmetry-equivalent ligands.

Table 1
Selected geometric parameters (A ˚, � ) for I.

Table 2
Close contacts (A ˚, � ) for I.

Synthesis and crystallization
Cis-(en) 2 Co(OSO 2 CF 3 )]CF 3 SO 3 (0.993 g, 1.57 mmol) and N,N-diethyl-N 0 -[(4-nitrobenzene)(oxo)methyl]carbamimidothioate (Weiqun et al., 2003) (0.524 g, 1.93 mmol) were added to 10 g of sulfolane, stoppered and stirred at room temperature (4 days) resulting in a dark-green solution.Extraction with one 100 mL portion of diethyl ether followed by two 100 mL portions of chloroform resulted in the formation of a maroon precipitate and dark-green solution.Evaporation of the diethyl ether/chloroform mixture resulted in deposition of dark-green crystals of the title complex (0.129 g, 9%).

Data collection, structure solution and refinement
On standard cold-N 2 gas stream cooling below about 100 K, all crystals of I could be indexed as primitive monoclinic, giving cell dimensions of approximately a = 16.6, b = 9.1, c = 44.1 A ˚, � = 100.6� , but many reflections were split and/or streaked, the severity of which varied from crystal to crystal.At room temperature, however, the symmetry was clearly trigonal or hexagonal, with sharp diffraction maxima.Attempts to 'lock in' the room-temperature structure by rapid cooling in liquid N 2 and mounting using cryotongs (Parkin & Hope, 1998) were unsuccessful.One such crystal, however, was monitored on slow warming at about 10 � per minute.By 180 K, all splitting/ streaking had disappeared.This crystal was used for data collection; details are given in Table 3. Structure solution (SHELXT; Sheldrick, 2015a) and refinement (SHELXL; Sheldrick, 2015b) were straightforward aside from the presence of severely disordered electron density in the channels running along [001].Modelling of this diffuse electron density as fractional-occupancy chloroform was less than satisfactory, perhaps because the presence of other species (e.g.water) could not be ruled out [water was modelled in the channels of DOVDOK and YIVROM (see section 4, above)].For this reason, the SQUEEZE routine (van der Sluis & Spek, 1990;Spek, 2015) in PLATON (Spek, 2020) was used to factor out the solvent contribution, which amounted to �12.5 electrons per asymmetric unit.

Special details
Experimental.The crystal was mounted using polyisobutene oil on the tip of a fine glass fibre, which was fastened in a copper mounting pin with electrical solder.It was placed directly into the cold gas stream of a liquid-nitrogen based cryostat (Hope, 1994;Parkin & Hope, 1998).The crystals underwent a reversible phase transition to a triply twinned incommensurately modulated phase when cooled to 90K.Visual inspection of crystal integrity and diffraction quality vs temperature established a safe temperature for data collection of -93° C. Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.Refinement progress was checked using PLATO (Spek, 2020) and by an R-tensor (Parkin, 2000).The final model was further checked with the IUCr utility checkCIF.

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Spackman et al., 2021) show that almost all intermolecular contacts (�96% of the total) involve hydrogen.These are shown in Fig.4, separated into H� � �H (36.6%),H� � �O (31.0%),H� � �C (19.2%),H� � �N (4.8%), and H� � �S (4.4%), including reciprocal contacts.All other types, i.e. those not involving hydrogen, have negligible coverage.4.Database surveyA search of the Cambridge Structural Database (CSD, version 5.45, update of March 2024;Groom et al., 2016) using a search fragment consisting of just the organic ligand, returned two hits: ZIMNOA(Saeed et al., 2013), a square-planar Ni II complex that contains two of the ligands and NOJWIV(Kuchar et al., 2019), a gold complex that has little else in common with I.A modified search with the NO 2 group replaced by 'any atom' gave 75 matches.A combined search using this same fragment, but restricted to only trigonal or hexagonal crystal systems resulted in four matches: DOVDOK(Barnard & Koch, 2019), YUFBIK(Bensch &  Schuster, 1995), YIVROM(Mandal & Ray, 2014), and VEMKIH(Sieler et al., 1990).These four structures are isotypic to I, and share the same space-group symmetry (P3).The most similar to I are entries DOVDOK and YUFBIK; each have cobalt as the metal centre, with -OMe and -H, respectively, in place of NO 2 .Structures YIVROM and VEMKIH contain iron and ruthenium, respectively, and similar to YUFBIK, have H at the 4-position of the benzene ring.Structures DOVDOK and YIVROM include water in the channels along [001].

Figure 3 A
Figure 3 A partial packing plot of I viewed approximately along [110] showing a column of molecules extending parallel to [001].

Figure 2 A
Figure 2 A packing plot of I viewed down [001], showing the extended channels running through the crystal along the c-axis direction.

Table 3
Experimental details.